Pass argc pointer to parse_options()

This lets us keep argc up to date as the backend picks out arguments
from the argv array.
diff --git a/clients/window.c b/clients/window.c
index d917550..249ba6f 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -4329,7 +4329,7 @@
 }
 
 struct display *
-display_create(int argc, char *argv[])
+display_create(int *argc, char *argv[])
 {
 	struct display *d;